1. Field of the Invention
The present invention relates to a syringe, and more particularly to a safety syringe, which has a ratchet device formed on the needle hub and an annular inclined teeth formed on one end of the plunger, such that when the hollow barrel is pushed toward the needle hub, the engagement between the ratchet device and the inclined teeth is able to pull the needle hub together with the needle inside the barrel when the barrel is pulled backward to prevent people from being punctured by the used needle.
2. Description of Related Art
A plastic cap is always mounted on the hollow barrel of a syringe to cover the needle to keep people from being punctured by the used needle. However, because the user must hold the conventional cap when he or she puts the cap onto the hollow barrel, the user is easily punctured by the needle. In addition, the used needle must be destroyed by melting or burning to prevent the spread of disease. However, hazardous gas will form when the needle with the plastic cap and needle hub is melted or burned.
In another conventional embodiment, a safety device is formed with the syringe to prevent the user from being punctured. Clamps are formed on the needle hub and the plunger of the syringe. When the plunger is fully pushed into the hollow barrel of the syringe, the clamps will engage with each other. The needle hub with the needle will release from and be pulled fully into the barrel when the plunger is pulled back. The used needle will be fully enclosed and held in the hollow barrel to keep the needle from touching or puncturing anyone.
However, a specific mold is required to form the clamps. The cost for manufacturing the syringe with the conventional safety device is expensive. In addition, because the entire syringe including the hollow barrel, plunger and the hub must be melted or burned with the needle, hazardous gas is still generated.
In order to reduce the fabrication cost, the market focuses on the development to introduce an improved syringe to pull the used needle inside the barrel. With reference to FIG. 1, a conventional safety syringe comprises a hollow barrel (10), a plunger (20), a needle hub (30) and a needle (40).
The needle hub (30) defines a receiving hole (301) in a rear end of the needle hub (30) and a shoulder (302) is formed inside the receiving hole (301). The plunger (20) has a conical head (201) formed on a front end of the plunger (20) to correspond to the receiving hole (301). With this arrangement, when the plunger (20) is moving inside the barrel (10) toward the needle hub (30) and eventually engages with the needle hub (30), the conical head (201) will have an interference fit inside the receiving hole (301). Because the formation of the shoulder (302), the conical head (201) is secured inside the receiving hole (301) after the plunger (20) is pushed all the way to the end of the hollow barrel (10), such that when the plunger (20) is pulled backward inside the barrel (10), the needle hub (30) together with the needle (40) is able to be pulled inside the barrel (10) simultaneously, as shown in FIG. 2.
However, to facilitate the needle hub (30) to be pulled inside the barrel (10), the engagement between the needle hub (30) and the barrel (10) should be loose otherwise the friction between the needle hub (30) and an inner periphery of the barrel (10) will overcome the connection between the plunger (20) and the needle hub (30) and the needle hub (30) can not be pulled back into the barrel (10) successfully. In the mean time, if the engagement between the needle hub (30) and the barrel (10) is loose, the solution inside the barrel will have a leak and the injection can not be successful. Further, when the needle (40) is inserted into a container (50) through the cork (51), the needle hub (30) may retract back into the barrel (10). However, if the engagement between the needle hub (30) and the barrel (10) is increased, the force required to pull the needle hub (30) together with the needle (40) back to the barrel (10) is also increased, which causes an extra burden to the users.
With reference to FIG. 5, whether reducing the diameter of the receiving hole (301) or increasing the diameter of the conical head (201) to increase the engagement force between the needle hub (30) and the barrel (10) will inevitably increase the difficulty of inserting the conical head (201) into the receiving hole (301) and this is the last thing that the user wants to see.
To overcome the shortcomings, the present invention intends to provide an improved safety syringe to mitigate or obviate the aforementioned problems.
The primary objective of the invention is to provide a syringe enabling to release the limitation of the barrel to the needle hub so that the needle hub with the needle is able to be pulled backward into the barrel easily.
Another objective of the invention is to provide a syringe that is able to provide a seal to the solution inside the barrel by the engagement between the needle hub and the barrel, such that there is no leak even though the needle hub is slidably engaged with the barrel.
Still, another objective of the invention is to provide an improved syringe with a ratchet device formed on one end of the needle hub and inclined teeth formed on one end of the plunger to correspond to the ratchet device of the needle hub, such that the engagement between the ratchet device and the inclined teeth will facilitate the retraction of the needle hub together with the needle back into the barrel.